JPS61153844A - Information recording medium - Google Patents

Abstract

PURPOSE:To prevent the whitening of a glass substrate and to improve the aging stability of a recording medium by forming a protective layer contg. an ultraviolet-curing resin on one side of the substrate having a recording layer on the other side. CONSTITUTION:The whitening of a surface of a glass substrate is remarkably reduced or prevented by forming a protective layer contg. an ultraviolet-curing resin on the surface of the substrate, and the aging stability of an information recording medium is improved. Alkali ions depositing on the surface of the glass substrate with the lapse of time are effectively diffused and captured in the protective layer to prevent the surface of the substrate from getting cloudy. Accordingly, the aging stability of the recording medium is improved, and especially when the writing and reading of information are carried out from the substrate side, reduction in the sensitivity and S/N can be prevented. Since the ultraviolet-curing resin in the protective layer has high hardness, the protective layer increases the scratch resistance of the recording medium and can prevent damage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention J The present invention relates to an information recording medium on which information can be written and/or read using a high energy density laser beam.

[Technical Background of the Invention and Prior Art] In recent years, information recording media that use high energy density beams such as laser light have been developed and put into practical use. This information recording medium is called an optical disk and can be used as a video disk, an audio disk, a large-capacity still image file, and a large-capacity computer disk memory.

The basic structure of an optical disk is a disc-shaped transparent substrate made of plastic, glass, etc., and a Bi
, a recording layer made of a metal such as Sn, In, Te, or a metal.

Information is written on an optical disk by, for example, irradiating the optical disk with a laser beam, and the irradiated portion of the recording layer absorbs the light and locally increases in temperature, causing physical or chemical damage. Information is recorded by causing changes in the optical properties of the optical fiber.

Reading information from an optical disk is also performed by irradiating the optical disk with a laser beam, and the information is reproduced by detecting reflected or transmitted light depending on changes in the optical characteristics of the recording layer. .

Recently, as a disc structure to protect the recording layer,
Consisting of two disk-shaped substrates, a recording layer is provided on at least one of the substrates, and a ring-shaped inner spacer is arranged between the two substrates so that the recording layer is located inside and a closed space is formed. An air sandwich structure has been proposed, in which a ring-shaped outer spacer is joined to the outer spacer. In optical discs with such a structure, the recording layer is not in direct contact with the outside air, and information is recorded and reproduced using laser light that passes through the substrate. Therefore, the recording layer is generally susceptible to physical or chemical damage. It has the advantage that there is no possibility of dust or dust adhering to its surface, which would impede information recording and reproduction.

Information recording media are highly useful in various fields as described above, but they are desired to be resistant to deformation, deterioration, etc., and to have good storage stability. In particular, when writing and reading information from the substrate side, such as in air-sand inch recording media, the substrate is not easily deformed or deteriorated due to issues such as recording sensitivity and recording accuracy. I hope so.

Conventionally, for the purpose of improving the deformation (solvent resistance, etc.) and impact resistance (scratch resistance, etc.) of the substrate of recording media,
It is known to provide a protective layer on the surface of the substrate opposite to the side on which the recording layer is provided. In other words, when a plastic material such as polymethyl methacrylate is used as the substrate material, the substrate is easily deformed by moisture in the atmosphere, and is easily damaged by mechanical shock. By attaching a protective layer made of photocurable resin or inorganic material to the surface of the plastic substrate, the surface hardness is increased and impact resistance is improved.

It has been proposed to improve the appearance and prevent deformation and deformation due to moisture absorption.

By the way, in addition to plastic substrates, glass substrates such as tempered glass can be used for binding the substrate of recording media. Compared to plastic substrates such as glass substrates, acrylic resins, and plastic resins, they are more susceptible to moisture absorption. The degree of deformation is small 1
, has great advantages such as high surface hardness and high shape stability over time.

However, in glass substrates, problems unique to glass arise that are different from those in the case of plastic substrates. That is, alkali metal ions such as Na, ``, ni+'' and alkaline earth metal ions such as Mg'' and C:a' (hereinafter collectively referred to as alkali ions) contained in the glass substrate are heated. Because it precipitates on the substrate surface due to the influence of humidity.

The surface tends to become cloudy over time. This clouding of the substrate surface (so-called white discoloration) causes a decrease in recording sensitivity and accuracy of information, and tends to deteriorate the stability of the recording medium itself over time.

[Summary of the Invention] An object of the present invention is to provide an information recording medium that prevents white discoloration of a glass substrate and has improved stability over time. - The above purpose is to provide an information recording medium having a recording layer on which information can be written and/or read by a laser on a glass substrate, with a radiation-curable This can be achieved by the information recording medium of the present invention, which is characterized by being provided with a protective layer containing a resin.

As a result of research on preventing white discoloration that occurs on the surface of a glass substrate, the inventor of the present invention found that by providing a protective layer containing a radiation-curable resin on the surface of the substrate.

The present invention has been made based on the discovery that it is possible to significantly reduce or prevent the occurrence of white discoloration on the surface of a substrate, thereby achieving a significant improvement in the stability over time of an information recording medium. It reached 1.

That is, according to the present invention, clouding of the substrate surface can be prevented by effectively diffusing and trapping alkali ions deposited on the glass substrate surface over time into the protective layer containing the radiation-curable resin. . Therefore, the stability of the recording medium over time is improved, and especially when information is written and read from the substrate side, it is possible to prevent a decrease in sensitivity and a decrease in the S/N ratio.

Further, since the radiation-curable resin used for the protective layer has high hardness, it is possible to improve the impact resistance (scratch resistance) of the recording medium and prevent damage. Furthermore, by adding the protective layer of the present invention, it is possible to solve the problem that fingerprints tend to adhere to the surface of the glass substrate.

Therefore, the recording medium of the present invention, which uses a glass substrate with excellent surface hardness, shape, and optical properties, and is provided with a protective layer that prevents white discoloration peculiar to glass, hardly causes deformation or deterioration of the substrate. It shows high stability over time.

[Structure of the Invention] The information recording medium of the present invention having the preferable characteristics as described above can be manufactured, for example, by the following method.

The substrate used in the present invention is a glass plate made of soda-lime glass or the like, and is particularly preferably a tempered glass plate with high surface strength.

Alkali ions (N a ”, K
A protective layer is provided in order to prevent clouding of the surface due to precipitation of ", M g ", Ca24, etc.).

The protective layer, which is a characteristic feature of the present invention, is a layer made of a radiation-curable resin.

The monomer (or oligomer or prepolymer) used in the radiation-curable resin in the present invention has double bonds such as acrylic double bonds and allylic double bonds, and undergoes a curing reaction when irradiated with ultraviolet rays or electron beams. As long as it has a double bond that can be
Acrylic acid, ethyl (meth)acrylate, butyl (meth)acrylate, ethylene glycol di(meth)acrylate, styrene, methylstyrene, acrylamide, glycidyl (meth)acrylate, maleic anhydride,
Diallyl maleate, diallyl adipate, cyclohexane acrylate, benzyl acrylate, N-methylol acrylamide, N-diacetone acrylamide,
2-Phenoxypropyl (meth)acrylate, carpitol acrylate, vinyl acetate, N-vinylpyrrolidone, ? -Ethylhexyl acrylate, 2-hydroxy acrylate, ? −
Hydroxypropyl acrylate, 2-hydroxyethyl acryloyl phosphate, 1,3-butanefold diacrylate, 1,4'-butanediol diacrylate, l,6-hexanethiol di(meth)acrylate, diethylene glycol di(meth)acrylate,
Tripropylene glycol diacrylate, neopentyl glycol diacrylate, polyethylene glycol 400 diacrylate, hydroxypivalic acid ester neopentyl glycol diacrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol triacrylate, dipentaerythritol hexaacrylate, butyl cellosolve Akurishiichito, α,
Examples include ω-diacrylbisethylene glycol tetrahydrophthalate, α,ω-tetraacrylbistrimethylolpropane tetrahydrophthalate, etc. As the oligomer or prepolymer, adipic acid/l, 6-hexanediol / Acrylic acid, phthalic anhydride / Propylene oxide / Acrylic acid, trimellitic acid / Diethylene glycol / (Unsaturated) polyester acrylate such as acrylic acid; Bisphenol A-epichlorohydrin type / Acrylic acid, phenol novolac epichlorohydrin type / Acrylic acid Epoxy acrylates such as alicyclic type/acrylic acid (where R is an alkylene group having 1 to 5 carbon atoms); polyurethane acrylates such as tolylene diisocyanate/polyester/2-hydroxy acrylate; other polyether acrylates; polyol acrylates ;Polyacetal acrylate and the like can be mentioned.

These 7-mers can be used alone or in a mixture of two or more. From the viewpoints of impact resistance (scratch resistance) and solvent resistance in addition to prevention of white discoloration on the substrate surface, particularly preferred among the above seven polymers are pentaerythritol diacrylate, pentaerythritol triacrylate, and bisphenol A. It is diacrylate.

The protective layer of the present invention may be made of only a radiation-curable resin, but it may be made of a mixture of a radiation-curable resin and a known thermosetting resin or thermoplastic resin depending on the purpose of the recording medium to be obtained. In that case, it is preferable that the radiation-curable resin is contained in the protective layer in an amount of 50% or more (volume ratio).

In forming the protective film, the radiation-polymerizable curable lacquer may be used alone, but if necessary, a polymerization initiator may be dissolved to prepare a coating solution (UV lacquer solution).

As a photopolymerization initiator, benzoin alkyl ether,
Examples include benzyl ketal, anatals, acetophenone derivatives, benzophenone derivatives, xanthone derivatives, thioxanthone derivatives, anthraquinone derivatives, and benzaldehyde derivatives. Specific examples of compounds that can be used as sensitizers include benzoin ethyl ether, benzoin isopropyl ether, benzoin butyl ether, benzophenone,
Benzyl, 2.2-dimethoxy-2-phenylacetophenone, 2.2-dimethoxy-2-hydroxyacetophenone, diphenyl disulfide, 2-hydroxy-2
-Propiophenone.

4.4°-bisdiethylaminobenzophenone.

Dimethylaminobenzaldehyde, ethyl-4°4°-
Examples include bisdimethylaminobenzophenone, ethyl anthraquinone, and 2-chlorothioxanthone. These sensitizers can be used alone or in appropriate combinations.

The monomer solution contains adhesion improvers such as silane coupling agents, antioxidants, stabilizers, and waterproofing agents.

Various additives such as fillers, inorganic substances, and antistatic agents can be added depending on the purpose.

Next, this coating liquid is applied onto the substrate by a coating method such as a spray method, a spinner method, a diruff method, a roll coating method, a blade coating method, a doctor roll method, or a screen printing method to form a coating film, and then electromagnetic radiation is applied. By irradiating the substrate with , the nitride in the coating film is polymerized and cured, and a protective layer is formed on the substrate.

The electromagnetic radiation used may include ultraviolet radiation, electron beams, etc. Among these, ultraviolet rays are preferred from the standpoint of equipment size, economy, safety, etc. In order to carry out the polymerization reaction more completely, irradiation with electromagnetic radiation is preferably carried out under vacuum or under a nitrogen gas atmosphere.

The thickness of the protective layer is generally 0. Ol to 1100 IL, preferably 0.5 to 50 ILm.

The surface of the substrate opposite to the AI preservation layer has improved planarity,
An undercoat layer (
Examples of the material of the undercoat Mi (or intermediate layer), which may be provided with (and/or intermediate layer), include polymethyl methacrylate, acrylic acid/methacrylic acid copolymer, styrene fist maleic anhydride copolymer, Polyvinyl alcohol, N-methylolacrylamide, styrene/sulfonic acid copolymer, chlorosulfonated polyethylene, polyimide, vinyl acetate/vinyl chloride copolymer, ethylene/vinyl acetate copolymer, polyester, polyethylene, polystyrene, polyurethane, cellulose rust conductor(
cellulose acetate, cellulose nitrate, etc.), polyhydroxystyrene, polyvinyltoluene, polyvinyl chloride, km
Examples include polymeric substances such as hydrogenated polyolefin, polypropylene, and polycarbonate; organic substances such as silane coupling agents; and inorganic substances such as oxides (Si02, A-203, etc.) and fluorides (MgFz, etc.).

In order to prevent alkali ions liberated from the substrate from diffusing into other layers, it is preferable to provide an undercoat layer made of a polymer having a woody group and/or a maleic anhydride group. In order to improve the 2-armor sensitivity and the signal-to-noise ratio, an intermediate layer of polymethyl methacrylate, nitrocellulose, polyhydroxystyrene or chlorinated polyolefin is preferably provided.

The undercoat layer (or intermediate layer) is formed by dissolving or dispersing the above-mentioned polymeric substance in a suitable solvent, and then applying this coating solution using a coating method such as spin code, dip coat, extrusion coat, bar code, or screen printing. It can be formed by coating it on a substrate. The layer thickness of the subbing layer is generally from 0.01 m to 20 m, preferably from 0.1 m to 10 m.

Furthermore, as the material for the intermediate layer, a photocurable polymer can be used for the purpose of forming grooves for laser beam tracking and unevenness representing information such as address signals. A typical example of the material used in that case is a mixture of a photopolymerizable monomer (oligomer) and a photopolymerization initiator. As a photopolymerizable monomer (oligomer).

Known materials such as methacrylic esters and acrylic esters such as ethylene glycol, polyethylene glycol, polypropylene glycol, trimethylolfuropane, and pentaerythritol can be used. Also as a photopolymerization initiator.

The photopolymerization initiators used in the above-mentioned protective layer can be used.

The intermediate layer is formed by first dissolving a polymerization initiator in the above photopolymerizable monomer, then applying this solution onto the substrate in the same manner as above to form a coating film, and then irradiating it with electromagnetic radiation such as ultraviolet rays. This can be carried out by polymerizing and curing the 7-mer.

Various additives such as antioxidants and stabilizers may be added to the above coating liquid (seven-summer solution) depending on the purpose.
The thickness of the intermediate layer formed in this way is generally 0.0
1 to 1100p.

Preferably it is 0 to 50 ILm.

A recording layer is then provided on the substrate (or subbing layer or intermediate layer).

Examples of materials used for the recording layer include Te, Zn,
In, SnA Zr, AIL, Ti, Cu, Ga, Au
, PL, and other metals; Bi, As, Sb, and other metalloids; Ge,
Semiconductors such as Si; and alloys thereof or combinations thereof may be mentioned. Also sulfides of these metals or metalloids.

Compounds such as oxides, borides, silicon compounds, carbides and nitrides; and mixtures of these compounds with metals can also be used in the recording layer. Alternatively, a combination of dyes and polymers can be utilized.

In the present invention, it is particularly preferable that the material of the recording layer is a mixture of In and GeS. In this case, the In content in the recording layer is in the range of 33.3 to 87.5% by weight. is preferred.

The recording layer is formed on the substrate by a method such as vapor deposition, sputtering, or ion blasting using the above-mentioned material. The recording layer may be a single layer or a multilayer, but the layer thickness is
In terms of optical density required for optical information recording, generally 10
The range is from 0 to 5,500 people, preferably from 200 to 1
The range is 000 people.

On the recording layer, for the purpose of improving mechanical strength, for example, natural polymeric substances such as gelatin and gelatin derivatives; synthetic polymeric substances such as cellulose derivatives, polysaccharides, latex-like vinyl polymers, and vinyl polymers, etc. A protective film may be provided.

In addition, in the above-mentioned bonded type recording medium,
It can be manufactured by bonding two substrates having the above structure using an adhesive or the like; in the case of an "air sandwich type" recording medium, at least one of the bases of the two disc-shaped substrates is A substrate having the above structure can be manufactured by bonding a ring-shaped back spacer and an inner spacer.

Next, Examples and Comparative Examples of the present invention will be described.

However, these customers do not limit the present invention.Evaluations on each side were performed as follows.

(1) Resistance to white discoloration: A sample consisting of a substrate with a protective layer (or only a substrate) was
The sample was placed in a constant temperature and humidity chamber at 90% RH and the number of precipitates generated was measured after 5 days. Using a 100x optical microscope, measure the number of precipitates generated within a K diameter of 2.5 mm at four locations, and the total is 0 to 2: A: 3 to 4 :B When 3 to 4 pieces: C When 11 or more pieces: D

(2) Impact resistance: A seven-foamed polystyrene sheet (thickness:
6mm) on top of the two layers.

A 132 g steel ball was dropped naturally from a height of 1.5 m vertically, and the impact strength was measured by the falling ball method.

Evaluation is if there was no destruction: A If there is a crack in a part: B If destroyed: C This was done in three stages.

(3) Fingerprint resistance: A right thumb fingerprint was placed on the surface of the protective layer (or substrate) of the sample. Separately, gauze was prepared that had been washed with special grade methanol and ultrapure water and then dried in a clean room, and the fingerprints were removed using this gauze. 'Next, the sample is irradiated with a He-Ne laser beam and its reflection is measured. -- When the fingerprint has completely disappeared: A When the fingerprint remains slightly: B When the fingerprint remains completely It was evaluated on a three-level scale with a rating of 20.

[Example 1] Disc-shaped soda lime glass plate (outer diameter: 300 mm, inner diameter: 35 mm) subjected to potash reinforcement treatment (depth: approximately 309 Lm)
, thickness: 1.3 mm) was washed with an alkaline solution and isopropyl alcohol, and dried.

Next, after preparing a coating solution by dissolving 3 parts by weight of benzoin methyl ether in 100 parts by weight of pentaerythritol triacrylate, a filter (pore size: 1 g,
m) and apply pressure 1! passed.

Apply this coating solution to the glass substrate using a spinner for 3 times.
Dropped at a rotational speed of 0 rpm, and gradually rotated. ! The obtained coated substrate was placed in a transparent box filled with nitrogen gas, and a 4KW ultra-high pressure mercury lamp was used.
The distance between the lamp and the substrate was set to 60 cm, and UV exposure was performed for 5 minutes to form a protective layer with a thickness of fOILm on the substrate (Sample 1).

Next, an intermediate layer made of polyethyl methacrylate having a layer thickness of 0°2#Lm was formed by a coating method on the surface of the glass substrate opposite to the side on which the protective layer was provided, and then
A recording layer having a thickness of 400 layers was formed by co-depositing 300 layers of In and 5,100 layers of Ge using a vacuum deposition method.

In this way, two substrates each consisting of a protective layer, a substrate, an intermediate layer, and a recording layer were manufactured in this order.

An information recording medium having an air sandwich structure was manufactured by placing these two substrates facing each other with the recording layer inside and bonding them together with the spacer.

[Example 2] Sample 2: A protective layer-attached substrate was prepared by performing the same procedure as in Example 1 except that bisphenol A diacrylate was used instead of pentaerythritol triacrylate in Example 1. ), and further, using this sample, an information recording medium with an air sandwich structure was manufactured.

[Example 3] A protective layer was attached by performing the same operation as in Example 1, except that α,ω-diacryl-bisethylene glycol tetrahydrophthalate was used instead of pentaerythritol triacrylate. Sample 3) was used to prepare a substrate, and this sample was used to produce an information recording medium with an air sandwich structure.

[Example 4] A protective layer was attached by performing the same operation as in Example 1 except that α,ω-tetraacrylbistrimethylolpropane tetrahydroacrylate was used instead of pentaerythritol triacrylate. A substrate was prepared (Sample 4), and this sample was used to manufacture an information recording medium having an air sandwich structure.

[Examples 5 to 7] Various protective layer-attached substrates were prepared in the same manner as in Example 1, except that mixtures having the following compositions were used instead of pentaerythritol triacrylate in Example 1. Samples 5 to 7) were prepared, and information recording media with an air sandwich structure were manufactured using these samples.

Sample DPEHA HPPA HENA IJA
SA 5iNHUV-)16 40 30
30 Q 3 1 3 Each compound used is as shown below.

DPEHA Nidipentaerythritol Hexaacrylate HPPA: 2-Hydroxy-3-phenoxypropyl acrylate HEMA: Exaethyl methacrylate UA
: Urethane acrylate SA : Silicone acrylate 5iNH Niaminosilane coupling agent UV-H : Benzyl [Comparative example 1] In Example 1, the same operation as in Example 1 was performed except that a protective layer was not provided on the surface of the glass substrate. By doing this, a glass substrate was prepared (Sample 8), and this sample was further used to manufacture an information recording medium with an air sandwich structure.

Table 1 shows the evaluation results for the above examples and comparative examples.

L no, T 2? Mi White Table 1 White discoloration resistance Impact resistance Fingerprint resistance Example I B B 82
8 B 83 B
B B4 B
A A5 CB A 6 CB B 7 B A B Comparative example I
D CC From the above results, the samples and information recording media (Examples 1 to 8) provided with a protective layer made of the radiation-curable resin of the present invention are different from the samples and information recording media (Comparative Example 1) not provided with a protective layer. ), it was clear that it was superior in white discoloration resistance, impact resistance, and fingerprint resistance.

Claims (1)

[Claims] 1. In an information recording medium having a recording layer on which information can be written and/or read by a laser on a glass substrate, radiation is applied to the surface of the substrate opposite to the side on which the recording layer is provided. An information recording medium characterized by being provided with a protective layer containing a curable resin. 2. The information recording medium according to claim 1, wherein the radiation-curable resin is a resin that is curable to ultraviolet rays. 3. The information recording medium according to claim 2, wherein the ultraviolet curable resin is an acrylic polymer. 4. The acrylic polymer contains (meth)acrylic acid ester of pentaerythritol and bisphenol A.
4. The information recording medium according to claim 3, wherein the information recording medium is a polymer of at least one photopolymerizable monomer selected from the group consisting of (meth)acrylic acid esters. 5. The information recording medium according to claim 1, wherein the information recording medium has an air sandwich structure.